VILLASnode/doc/Tuning.md

# Tuning {#tuning}

This page is not directly related to VILLASnode.
It describes several ways to optimize the host system for running real-time applications like VILLASnode.

## Operating System and Kernel

For minimum latency several kernel and driver settings can be optimized.
A [PREEMPT_RT patched Linux](https://rt.wiki.kernel.org/index.php/Main_Page) kernel is recommended.
Precompiled kernels for Fedora can be found here: http://ccrma.stanford.edu/planetccrma/software/

1. Tune overall system performance for real-time:

1.1. Use the `tuned` tool for imprving general real-time performance.

Please adjust the setting `isolated_cpucores` according to your hardware.

```bash
$ dnf install tuned-profiles-realtime
$ echo "realtime" > /etc/tuned/active_profile
$ echo "isolated_cpucores=6-7" >> /etc/tuned/realtime-variables.conf
$ systemctl enable tuned && systemctl start tuned
```

This enables the following `tuned` profiles:

 - latency-performance
   - network-latency
     - realtime

1.2 Install a `PREEMPT_RT` patched Linux kernel.

2. Optimize the VILLASnode configuration
2.1. Map NIC IRQs	(see global setting `affinity`)
2.2. Map Tasks (see global  setting `affinity`)
2.3. Increase priority of server task (nice(2)) (see global setting `priority`)
2.4. Increase BSD socket priority (see global setting `priority` for  node-type `socket`)

3. Configure NIC interrupt coalescence with `ethtool`:

```bash
$ ethtool --coalesce eth0 adaptive-rx off adaptive-tx off
```

4. Configure NIC kernel driver in `/etc/modprobe.d/e1000e.conf`:

```
# More conservative interrupt throttling for better latency
# https://www.kernel.org/doc/Documentation/networking/e1000e.txt
option e1000e InterruptThrottleRate=
```

## Hardware

This are some proposals for the selection of appropriate server hardware:

- Server-grade CPU: Intel Xeon
  - A multi-core systems enable true paralell execution of multiple send / receive paths.

- Server-grade network cards: Intel PRO/1000
  - These allow offloading of UDP checksumming to the hardware